The present invention relates to an improved insole for footwear. More particularly, the present invention is an insole with a cavity for housing a heat source. The insole is adapted to maximize circulation of air to the heat source and maximize circulation of the heat produced thereby to the wearer""s entire foot.
It is desirable to provide an effective, inexpensive, safe, convenient and comfortable way to keep a person""s feet warm in cold environments. A variety of devices and methods are known for this purpose. For example, footwear can be provided with insulation or made waterproof. Such methods have significant drawbacks. For example, waterproofing methods provide no manner of either retaining heat or providing additional heat to the wearer""s feet. Rather, they only prevent the introduction of water or other liquid which could make the wearer""s feet cold. Insulation is largely ineffective as well because it merely retains body heat without providing any additional heat.
One known method of providing a heat source in footwear involves placing an electric heating element in the shoe or boot liner and using a battery to supply energy to the heating element. Another attempt to solve the problem of cold feet has involved the use of electrical heating elements in socks. Foot warming devices that use electric heating elements have a number of disadvantages. First and foremost, they are dangerous. Specifically, they create the risk of electric shock, sparks that could cause flammable socks and/or footwear materials to catch fire which in turn could burn the wearer""s feet, and electrical shortages. Such electrical devices are also expensive and inconvenient to use. The batteries for such devices are expensive and require long recharging times to be effective. Batteries can also leak and cause damage to the footwear and/or burn the skin of the user. Battery packs are bulky, add unnecessary weight for the user to carry and may interfere with the user""s movements. A battery has the additional disadvantage that as the ambient temperature decreases, the battery""s power output decreases. Therefore, as the need for heat increases, the battery powered systems decrease in effectiveness.
It has also been known to adapt the insoles of boots, shoes and the like to accommodate a heat dispensing material in a pocket formed in the insole. These devices also have significant disadvantages. Specifically, they all contemplate permanently modifying the footwear itself to accommodate the heat dispensing material. This could permanently add weight and bulk to the footwear which is unnecessary, especially when the footwear is worn in warm environments. In addition, these devices do not allow for adequate circulation of the generated heat to the wearer""s feet.
U.S. Pat. No. 5,230,170, issued Jul. 27, 1993 to Dahle discloses a removable insole for footwear that has a reduced thickness portion in the padding layer creating a cavity for holding a heat source that produces heat from an exothermic chemical reaction. The insole disclosed in Dahle has an upper layer that has a plurality of holes for facilitating heat transfer from the heat source to the wearer.
Although an improvement over the prior art, the insole disclosed by Dahle also has significant drawbacks. First and foremost, the heat source is enclosed in the cavity in such a way that the amount of air that can reach the heat source is limited. Thus, because the heat source needs oxygen to drive the chemical reaction necessary to generate heat, the amount of heat produced is greatly inhibited. The heat source is also enclosed in the cavity in such a way that the heat generated by the heat source cannot adequately circulate so that the wearer""s feet are not effectively heated. Further, Dahle discloses that the heat source is enclosed at its lower side by a cover plate of rigid material. The shape, size and manner in which this cover plate is connected to the insole create a propensity for the cover plate to tear away from the insole during wear, requiring the wearer to either repair or replace the insole. Further, because of the structure of the cavity, it is difficult to insert and remove the heat source from the cavity in the insole disclosed by Dahle.
It is desirable to provide an insole which overcomes the above-stated disadvantages.
In accordance with the present invention, there is disclosed an improved removable insole that provides an effective, inexpensive, safe, convenient and comfortable way to keep a person""s feet warm in cold environments.
Preferably, the improved insole is formed in the general shape of the outline of the human foot, thereby having a toe portion, an arch portion and a heel portion, so that the insole can be inserted into a boot or shoe. In a preferred embodiment, the arch and heel portions contour the shape and position of the wearer""s arch and heel to thereby provide support for the wearer""s arch and heel.
In a preferred embodiment, the improved insole has a recessed area in the toe portion for containing a heat source. Preferably, the improved insole has an upper layer and a padding layer having an upper side connected to a lower side of the upper layer. The improved insole also preferably has a lower layer, having an upper side connected to the lower side of the padding layer. In one embodiment, the lower layer is comprised of two parts. A first part of the lower layer is formed of a pliable material, to allow for easy flexing of the toe portion during wear, and extends from the tip of the toe portion to at least past the end of the recessed area furthest from the toe portion and preferably almost to the arch of the foot. A second part of the lower layer is formed of a rigid material for durability and support, and extends from the end of the first part of the pliable lower layer to the heel portion.
Alternatively, the improved insole has a lower layer covering only a portion of the insole, formed of a rigid material for durability and support. Said lower layer extends from the heel portion to just before the edge of the recessed area furthest from the toe portion.
In the preferred embodiment, the recessed area is formed by an area of reduced thickness in the padding, upper and/or lower layer(s).
In the improved insole, a cover plate may be attached to the lower side of the insole. The cover plate extends from the tip of the toe portion to at least past the end of the recessed area furthest from the toe portion. The cover plate conforms to the shape of the insole in that section. In the improved insole, an enclosed area is thereby formed for containing a heat source. The heat source may be a commercially available device that produces heat from an exothermic chemical reaction.
The cover plate is preferably formed of a rigid material to stabilize the heat source and maintain it in a predetermined configuration to assure comfort to the wearer""s foot. The cover plate is preferably not continuously attached to the insole along the cover plate""s periphery or across its width, but rather is attached to the insole in a number of discrete locations forward of the recessed area and a number of discrete locations rearward of the recessed area. Such a method of attachment allows air to freely enter and exit the recessed area for improved reaction with the chemicals in the.heating element and distribution of the generated heat to the wearer""s entire foot.
The insole preferably has a plurality of holes therein in the area above the recessed area for further facilitating heat transfer from the heat source to the foot of the wearer.
The lower side of the insole preferably has two sets of recessed channels formed therein that run parallel to the length of the foot. One set of recessed channels runs from the tip of the toe portion to the edge of the recessed area closest to the toe portion. The second set of recessed channels run from the edge of the recessed area furthest from the toe portion toward the heel portion, which recessed channels meet in another recessed portion of the lower layer near the heel. Such recessed channels further improve the circulation of air to the heat source to react with the chemicals in the heat source, and improve the circulation of heat from the heat source to the entire foot. The recessed portion in the lower layer near the heel also provides a cushioning effect to the wearer by absorbing shock as the wearer walks. Further, the recessed portion in the lower layer near the heel may change in volume pushing air toward the heat source and drawing heated air from the heat source toward the heel, thereby facilitating heating of the wearer""s entire foot.
The improved insole also preferably has at least one cutout on at least one of the sides of the recessed area, so that upon insertion of the heat source in the recessed area, the edge of the heat source will protrude beyond the edge of the insole at the cutout, thereby allowing for easy insertion and removal of the heat source.